1. Field of the Invention
The present invention relates to a hydraulic pressure supply system of an automatic transmission for a vehicle. More particularly, the present invention relates to a hydraulic pressure supply system of an automatic transmission for a vehicle that supplies necessary pressure to a necessary portion by using a mechanical hydraulic pump having a low-pressure discharge port and a high-pressure discharge port, and minimizes driving loss of the hydraulic pump and improves fuel economy by returning unnecessary hydraulic pressure.
2. Description of Related Art
Recently, vehicle makers direct all their strength to improve fuel economy due to worldwide high oil prices and strengthening of exhaust gas regulations.
Improvement of fuel economy may be achieved by improving power delivery efficiency, and the improvement of the power delivery efficiency may be achieved by minimizing unnecessary power consumption of a hydraulic pump.
A recent automatic transmission is provided with a low-pressure hydraulic pump and a high-pressure hydraulic pump so as to improve fuel economy. Therefore, hydraulic pressure generated by the low-pressure hydraulic pump is supplied to a low pressure portion (i.e., a torque converter, a cooling device, and a lubrication device), and hydraulic pressure generated by the high-pressure hydraulic pump is supplied to a high pressure portion (i.e., friction members selectively operated when shifting).
In further detail, general hydraulic pressure of the automatic transmission is generated for the low pressure portion (i.e., generated by the low-pressure hydraulic pump), and hydraulic pressure demanded by the high pressure portion is generated by the high-pressure hydraulic pump and then is supplied to the high pressure portion.
Therefore, fuel economy may be improved by minimizing power consumption for driving the hydraulic pump, and noise and vibration may be reduced and durability may be improved by reducing load applied to the hydraulic pump.
In the hydraulic pressure supply system, the low-pressure hydraulic pump and the high-pressure hydraulic pump are driven by one drive shaft, or the low-pressure hydraulic pump is driven by driving torque of an engine and the high-pressure hydraulic pump is driven by driving torque of a motor.
If both of the low-pressure hydraulic pump and the high-pressure hydraulic pump are used, structure of the automatic transmission may be complex and weight may be increased.
In addition, if two hydraulic pumps are used, manufacturing cost may increase and mountability may be deteriorated.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.